With Florida bracing for a monster Hurricane Irma after Harvey devastated Texas, money for the U.S. Federal Emergency Management Agency could be depleted before month's end or sooner, despite a government top-up of $7.4 billion that was approved on Friday.

Based on the "burn rate" of relief funds, cash that's used for rebuilding roads and bridges and for distributing bottled water, medical supplies, food and baby formula should be gone before Sept. 30, when government funding expires and a new fiscal year begins.

Compounding the problem is the fact Irma is forecast to batter highly developed parts of Florida, while Hurricane Jose gathers strength over the Atlantic Ocean.

"FEMA can easily go through $200 million a day, just co-ordinating and doing relief," said Elizabeth Zimmerman, a former associate administrator at the agency during the Obama administration.

"They were burning through that amount just doing that with Harvey. Now with Irma coming through, it's going to cost even more."

Irma isn't expected to bring as much rain as Harvey, she said, but storm surge impacts and flooding could make it even "more costly" in the long term than Harvey, which Texas's governor estimates will cost up to $180 billion when all the damage is tallied.

Irma and Harvey could cost a combined $400 million a day in relief. By that calculation, FEMA could spend more than $8 billion in the 21 days between now and Sept. 30 — more than it will have in its cash box with the $7.4-billion injection.

FEMA's disaster relief fund reportedly had only $1.01 billion left last Tuesday. It was expected to be fully drained by this weekend.

'Won't even make a dent'

But a lifeline came on Friday: The U.S. House of Representatives passed a $15-billion relief package, with half the funds dedicated to community development block grants; the other half to FEMA.

"It's on its way to the president's office, and I would expect him to sign this immediately upon receipt, since it was the president who was expecting this," Zimmerman said.

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Shoppers encounter empty bread shelves at a supermarket in Kissimmee, Fla., ahead of the expected arrival of Hurricane Irma. (Gregg Newton/Reuters)

FEMA's budget must be replenished when the new fiscal year begins in October. A total of $6.7 billion was allocated for disaster relief in the 2017 budget.

The annual disaster relief fund is calculated based on a formula of cost expended over the previous decade. The money is for ongoing rebuilding efforts from other disasters, such as last year's flooding in Baton Rouge, La., or the Tennessee floods of 2010. Wildfires currently burning in the western U.S. could also draw from the same fund.

Former FEMA director James Lee Witt, who ran the agency during the Bill Clinton administration, says the $7.4-billion re-up "won't even make a dent" in Harvey relief efforts.

"With Harvey alone, it's probably going to cost as much or more than [2005's Hurricane] Katrina was, and then add Irma on top of that, which is maybe going to be equally as much as Harvey," he said.

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U.S. President Donald Trump and first lady Melania Trump help volunteers hand out meals during a visit with flood survivors of Hurricane Harvey at a relief centre in Houston last weekend. (Kevin Lamarque/Reuters)

Witt criticized the White House's "America First" budget blueprint in March, which proposed slashing $700 million in FEMA grants, a prospect that now seems less likely.

"How could you cut that money out of an agency that has a responsibility to help state and local governments and people recover their lives and their livelihoods?" he said.

In the event that FEMA disaster relief funding actually runs out before the next fiscal year, it's not as if officials would pack up and leave or stop trucking in supplies, said Scott Knowles, a disaster historian at Drexel University in Philadelphia.

That would be a "crazy situation," he said. "Imagine the fire department came to your house to put out a fire, and in the middle of fighting the fire, they said, 'We just ran out of money. We need to go back to city hall to pay for the fire truck.'"

If FEMA runs out of money, as it did during the Hurricane Irene disaster in 2011, workers would likely continue on as usual, though they would technically be in breach of the Antideficiency Act, which prohibits federal spending of money that hasn't been appropriated. (Nobody has ever been prosecuted for violating the statute, according to the Center for Public Integrity.)

'Serious bind'

But a lack of money could complicate or slow rebuilding efforts for, say, the contracting-out of workers for debris removal, said Ken Burris, the former FEMA chief operating officer who worked with Witt.

"State and local governments would not be able to receive any reimbursement expenses, which puts everybody into a serious bind."

Burris stressed that the public shouldn't be naive about how expensive recovery efforts can be. During the cleanup for Hurricane Katrina in New Orleans, "we had a burn rate where we spent a billion dollars a day, for five days," he said.

Depending on the extent of the damage caused by Irma, he wouldn't be surprised if relief ends up costing $500 million a day in the immediate aftermath.

Barry Scanlon, former director of corporate affairs for FEMA under Clinton, also doubts the supplemental money will last until October. He expects another relief bill will be needed soon, with more to follow.

"They're going to be coming back two, three, four times maybe to do this," he said. "They were going to have to do it again for Harvey anyway, never mind Irma."

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Mike McCorkle examines a pile of debris out front of his house in Bellaire, Texas, following Hurricane Harvey. There's concern Hurricane Irma could cause similar destruction in Florida. (Nick Carey/Reuters)

Experts have noted it wasn't even peak hurricane season yet when this year's relief fund got close to being empty. Climate scientists attribute some of the intensity of the strong hurricanes brewing over the Atlantic to climate change.

Historian Knowles says current funding levels for FEMA disaster relief are "just not sufficient."

"It's hard to plan for two Category 5 storms to hit in one month just before October, but this is the new normal."

Weeks before Harvey made landfall, U.S. President Donald Trump revoked an executive order imposed by his predecessor, Barack Obama, requiring new building standards for federally funded infrastructure. The policy was meant to mitigate flooding risks so that reconstruction would have to conform to updated codes and not occur on flood plains, for instance.

Trump's decision to rescind the restrictions upset some taxation experts, who said the rollback is penny-wise and pound foolish.

As the country grapples with potentially hundreds of billions of dollars worth of reconstruction ahead, the administration is reportedly considering whether to re-implement the Obama-era requirements.